Adjustable inductor



Nov. 25, 1969 w. E. NEUMAN ADJUSTABLE INDUCTOR Filed Nov. 1, 1967 UnitedStates Patent 3,480,896 ADJUSTABLE INDUCTOR Werner E. Neuman, Deerfield,Ill., assignor to Components Corporation, Chicago, Ill., a corporationof Illinois Filed Nov. 1, 1967, Ser. No. 679,798 Int. Cl. H01f /02,21/06, 27/02 US. Cl. 336-83 3 Claims ABSTRACT OF THE DISCLOSUREBackground of the invention High Q coils of the type under considerationhere are formed of two, facing, annular, cup cores wherein the outsiderings or walls abut and the inside rings or walls stand somewhat apart.A winding is contained in the an nular space between the inner and outerwalls. A tuning slug fits closely within the sleeve defined by the innerrings and is adjustable to span the gap between the inner rings or to bevariably displaced from such spanning position.

Inductors of this character must be assembled with great care. The gapbetween the inner rings is critical and the avoidance of stresses withinthe core structure is critical. Else, the permeability of the core willdrift and vary over a period of time. At the same time, the inductorsmust be proof against a certain amount of shock incident to handling,use in mobile equipment, etc. Consequently, a problem resides in thesimple assembly of an inductor of this character whereby the parts aresecured firmly and accurately together without the imposition ofdistorting stresses.

Likewise, of course, it is highly important that the tuning slug, whenonce adjusted, remain in its adjusted position and not be subject todisplacement therefrom by vibration or shock. As a part of this sameconsideration, it is desirable that the tuning slug be periodicallyadjustable from one position to another and retain its same resistanceto accidental dislocation between such changes.

With regard to the latter consideration, it should be appreciated thatfor maximum reactance and maximum variation, the clearance of the slugis such as to preclude the existence of any intervening material betweenthe slug and the inside sleeve.

Summary of the invention The invention here is directed to a shockprooftunable inductor of the type described including a novel form ofassembly and a novel provision for tuning slug adjustment, the latter ofwhich is not only proof against shock but capable of unlimitedreadjustment without losing its strong frictional drag characteristicswhich maintain the tuning slug in position.

Brief description of the drawings FIG. 1 is a perspective view of aninductor embodying my invention;

FIG. 2 is a vertical section through the inductor of FIG. 1 taken alongline 2-2 of that figure looking in the direction of the arrows; and

FIG. 3 is a transverse section taken along the line 33 of FIG. 2 lookingin the direction of the arrows.

Description of the preferred embodiment The inductor considered includestwo substantially identical annular cup cores 10 and 12 desirably formedof a ceramic ferrite sufficiently dense and solid as to have negligibleor no water absorbing capability, although, for some purposes, sinterediron is suitable. The cores include an annular base 14 and inner andouter cylindrical walls 16 and 18 extending alike from the inner andouter peripheries of the base 14 respectively. The inner walls areshorter than the outer walls. The lower core 10 will have its basenotched out as at 20 at one or more discrete points through the outerperiphery inwardly beyond the outer wall 18. A winding 22 on a spool orbobbin 24 is inserted into the annular cavity of the lower cup core 10to surround and stand above the inner wall thereof. The upper cup coreis inverted and inserted into the upper end of the spool with the innerwall contained within the axial aperture of the spool. The relationshipof the cores to the spool is such that the outer walls of the corescontact each other and the inner walls stand somewhat spaced from eachother defining an annular gap 26. The leads 28 of the coil 22 are passedthrough the notches 20 for appropriate electrical connection.

The lower core rests on the rim 30 of a shallow, cuplike base formed ofmolded or machined plastic 32. The diameter of the rim is equal to thatof the core and the wall thickness of the rim is approximately equal tothat of the outer wall of the core. The base has terminal pins 34 moldedor assembled therein extending above and below the bottom 36 thereof towhich the coil leads 28 are soldered within the cup. Externally, thebase has a peripheral recess formed above its lower edge to define anannular ledge 38 parallel to the rim 30 of the base.

The inductor is bound together as a unit by a can 40 An 0 ring 42 ofsynthetic rubber having a diameter equal to the outside diameter of thecup cores 10 and 12 is placed on the top cup core and the inverted can40 placed over the entire, stacked assembly of the tWo cup cores and thebase, with the bottom 44 thereof bearing against the O ring and thecylindrical sides 46 extending down beyond the ledge 38 of the base.Thereafter the free edge 48 of the can is rolled inwardly as by spinningor the like to engage the ledge 38 and exert a compressive force againstthe outer edges of the cup cores and the base through the resilientmedium of the O ring 42 to contain the whole structure firmly together.The O ring in this assembly contributes several desirable effects: itholds the two cup cores tightly together in straight compression alongtheir outer edges for optimum magnetic coupling; it loads resilientlythe engagement of the spun edge 48 against the ledge 38 for optimumtightness; it makes the assembly shake-proof; and it achieves all thiswithout the application of pressure on the cup cores inwardly of theouter edges which might tend to distort the cores and interfere with thepredictable values of the inductor.

In the illustrated inductor, a tuning slug 50 of ceramic or sinterediron is employed which fits very closely within the sleeve defined bythe inside walls 16 of the cup cores for optimum coupling and a maximumrange of values. This exceedingly close fit prohibits the use ofmaterial intervening between the inside wall of the cup core and thetuning slug, and imposes the requirement that adjusting engagementbetween core and slug be made axially away from the slug.

As shown here, the tuning slug 50 is a tubular member having a centralaperture 52 therethrough. A fibre glass rod 54 is machined to have athreaded lower end 56, a flange 58 upwardly of the threaded portion, anda small diameter stem 60 receivable closely within the bore 52 of theslug 50. The stem extends upwardly above the slug. A brass cap 62 ispress-fitted on the upwardly extending end of the stern above the slug,and desirably cemented thereto, in tight contact with the slug so thatthe slug is confined between it and the flange 58. The cap is crossslotted at its top end as at 64 for adjustment by a screwdriver blade.The can 40 has an aperture 66 in the center of the base thereof throughwhich screwdriver access to the cap is provided. The aperture 66 issmaller than the cap 62 so that the can constitutes a stop for theadjustment of the slug when the slug is wholly withdrawn from the gap.

A tubular, flanged nylon nut 68 is press-fitted and ad hesively securedwithin the lower end of the aperture of the lower cup core with theflange 70 thereof bearing against the base of the cup core. The threadedend 56 of the stem 54 is engaged in the nut. The nut need not bethreaded. The fibre glass is sufficiently hard to impress its ownthreads into the softer nylon material. The engagement of the fibreglass threads with the nylon nut provides a high component of frictionalresistance to accidental movement of the stem within the nut, and thusanchors the slug against accidental displacement while permitting anunlimited number of adjustments without lessening frictional holding.

This effect is attainable through the employment of the fibre glassstem. In a characteristic embodiment of this invention, the insidediameter of the sleeve will be about .122 inch and the outside diameterof the tuning slug will be about .115 inch. The aperture thereforethrough which the stem must extend is exceedingly small, about .038inch, and with the frictional engagement sufficient to hold the slug inits adjusted position to meet the vibration resistant qualifications, asubstantial torsional force of adjustment must be transmitted throughthe very small diameter stem. Fibre glass possesses the requisitetorsional strength, is easily machinable, is nonmetallic, and is aunique and practical answer to the problem. A machined brass equivalentto the fibre glass stem has been employed successfully in the practiceof this invention. The strength of the brass may be superior to thefibre glass. However such substitution results in a 10 to 20% increasein the loss of the inductor at some frequencies.

Although a single embodiment only has been described of this inventionit should be appreciated that this embodiment is set forth only by wayof illustration and not .4 by way of limitation and that this inventionshould be regarded as being limited only as set forth in the fo1- lowingclaims.

I claim:

1. A tunable inductor comprising a pair of annular cup cores, eachhaving an outer wall and a shorter inner wall extending alike from theoutside edge and the inside edge respectively of an annular base, thefree edges of said outer walls meeting, a winding contained in theannular space between said inner and outer walls, means securing saidcores together in said relationship, a cylindrical tuning slug having anaxial bore therethrough within said inner walls, and means for movingsaid slug variably across the gap between the inner walls of said coresincluding-a shaft of a material strong in torsion extending through saidslug bore and providing a shoulder, means anchoring said slug againstsaid shoulder, said shaft extending beyond said shoulder in a threadedextension, and a nut in one of said inner walls beyond said gap engagingsaid threaded extension with high frictional resistance to rotation,said shaft having means at the free end thereof for effecting rotationthereof.

2. The combination as set forth in claim 1 wherein said nut is anunthreaded, relatively soft, deformable polymer, impressible by saidextension to define matching threads.

3. The combination as set forth in claim 1 wherein said shaft ismachined fibre glass.

References Cited UNITED STATES PATENTS 2,221,217 11/1940 Kink et a1.336136 XR 2,608,610 8/1952 Thulin 336-83 XR 2,669,700 2/1954 Ranch336-83 XR 2,946,029 7/1960 Abrams et al. 33683 XR 3,027,527 3/1962 West336-- 3,162,829 12/1964 Wildy et al. 336-83 3,197,167 7/1965 Stungis336-83 LEWIS M. MYERS, Primary Examiner T. J. KOZMA, Assistant ExaminerU.S. C1. X.R. 336136, 92

